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Innate Immune System of Mallards (Anas Platyrhynchos)

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Innate Immune System of Mallards (Anas Platyrhynchos) Anu Helin Linnaeus University Dissertations No 376/2020 Anu Helin Eco-immunological studies of innate immunity in Mallards immunity innate of studies Eco-immunological List of papers Eco-immunological studies of innate I. Chapman, J.R., Hellgren, O., Helin, A.S., Kraus, R.H.S., Cromie, R.L., immunity in Mallards (ANAS PLATYRHYNCHOS) Waldenström, J. (2016). The evolution of innate immune genes: purifying and balancing selection on β-defensins in waterfowl. Molecular Biology and Evolution. 33(12): 3075-3087. doi:10.1093/molbev/msw167 II. Helin, A.S., Chapman, J.R., Tolf, C., Andersson, H.S., Waldenström, J. From genes to function: variation in antimicrobial activity of avian β-defensin peptides from mallards. Manuscript III. Helin, A.S., Chapman, J.R., Tolf, C., Aarts, L., Bususu, I., Rosengren, K.J., Andersson, H.S., Waldenström, J. Relation between structure and function of three AvBD3b variants from mallard (Anas platyrhynchos). Manuscript I V. Chapman, J.R., Helin, A.S., Wille, M., Atterby, C., Järhult, J., Fridlund, J.S., Waldenström, J. (2016). A panel of Stably Expressed Reference genes for Real-Time qPCR Gene Expression Studies of Mallards (Anas platyrhynchos). PLoS One. 11(2): e0149454. doi:10.1371/journal. pone.0149454 V. Helin, A.S., Wille, M., Atterby, C., Järhult, J., Waldenström, J., Chapman, J.R. (2018). A rapid and transient innate immune response to avian influenza infection in mallards (Anas platyrhynchos). Molecular Immunology. 95: 64-72. doi:10.1016/j.molimm.2018.01.012 (A VI. Helin, A.S., Wille, M., Atterby, C., Järhult, J., Waldenström, J., Chapman, N A S J.R. (2018). Expression of immune genes RIG-I and Mx in mallard duck PL infected with low pathogenic avian influenza (LPAI): A dataset. Data in A TYRHYNCHOS Brief. 18: 1562-1566. doi:10.1016/j.dib.2018.04.061 Lnu.se isbn: 978-91-89081-33-8 (print), 978-91-89081-34-5 (pdf ) ) linnaeus university press Eco-immunological studies of innate immunity in Mallards (Anas platyrhynchos) Linnaeus University Dissertations No 376/2020 ECO-IMMUNOLOGICAL STUDIES OF INNATE IMMUNITY IN MALLARDS (ANAS PLATYRHYNCHOS) ANU HELIN LINNAEUS UNIVERSITY PRESS Eco-immunological studies of innate immunity in Mallards (Anas Platyrhynchos) Doctoral dissertation, Department of Biology and Environmental Science, Linnaeus University, Kalmar, 2020 ISBN: 978-91-89081-33-8 (print), 978-91-89081-34-5 (pdf) Published by: Linnaeus University Press, 351 95 Växjö Printed by: Holmbergs, 2020 Abstract Helin, Anu (2020). Eco-immunological studies of innate immunity in Mallards (Anas platyrhynchos), Linnaeus University Dissertation No 376/2020, ISBN: 978-91- 89081-33-8 (print), 978-91-89081-34-5 (pdf). Written in English with a summary in Swedish. This thesis comprises two sections, both of which explore eco-immunology of the innate immune system of mallards (Anas platyrhynchos). The innate immune system serves a pivotal role as the first line of defense against invading pathogens, and is comprised of physical and chemical barriers. Its main function is to inhibit and/or eliminate the pathogenic microorganisms while minimizing collateral damage to host cells. The first section investigates the allelic variation and selective forces acting on five avian -defensin (AvBD) genes. Showing that purifying selection is the predominant selective force, although one gene AvBD3b, appeared to be subject to balancing selection. Moreover, the solution structure of the AvBD3b peptide was solved in this work, revealing that it contains a typical -defensin fold with three -sheets. Linear and folded AvBD3b peptides were shown to exhibit similar antibacterial properties, indicating that the tertiary structure was not the primary determinant of antimicrobial activity. Moreover, testing the antimicrobial activity of synthetic AvBD peptides showed that they mostly had higher activity against Gram-negative than Gram-positive bacteria. The second section investigates expression of two innate immune genes during avian influenza virus infection. Data quality in gene expression studies depends, in part, on the stability of the reference genes (RGs) used to normalize expression levels, meaning putative RGs must be validated prior to use. Eleven potential mallard RGs were tested and it was found that the stability varied across different tissue types, highlighting the importance of correct RG selection for the specific experimental conditions. Optimal RGs were then used in a gene expression study of retinoic acid inducible gene 1 (RIG-I) and myxovirus resistant gene (Mx) in mallards during a low pathogenic avian influenza (LPAI) infection. Upregulation of both genes was rapid and transient, returning back to basal levels two days post infection across most of the five tissue types analyzed. This thesis provides new insights into the tertiary structure and antimicrobial activity of AvBDs, and how this relates to selective pressures exerted in natural populations. It also highlights the importance of RGs validation, and confirms that RIG-I and Mx are involved in the early stages of the mallard immune response to LPAI infection. Keywords: Avian -defensins (AvBDs), Avian gene expression, Host-pathogen interactions, Innate immunity, Mallard (Anas platyrhynchos), Myxovirus resistance gene (Mx), Retinoic acid inducible gene 1 (RIG-I) Svensk sammanfattning Den här avhandlingen består av två delar, vilka fokuserar på olika delar av det medfödda immunförsvaret hos gräsand (Anas platyrhynchos). Det medfödda immunförsvaret består av fysiska och kemiska barriärer vars uppgift är att hindra patogener att infektera kroppens celler, och att vid infektion eliminera dem. Första delen undersöker allelvariation och selektion hos generna för fem olika -defensiner (AvBD) hos gräsand och andra änder. Studierna visade att stabiliserande urval är den dominerande selektionskraften för dessa gener utom för AvBD3b, som var föremål för balanserande selektion. Den tredimensionella strukturen för AvBD3b bestämdes och uppvisade en generell -defensinstruktur innehållande tre -flak. Syntetiserade linjära och veckade AvBD3b-peptider hade liknande antibakteriella egenskaper, vilket antyder att den tredimensionella strukturen inte är avgörande för den antibakteriella funktionen. Den antibakteriella aktiviteten hos ytterligare fem AvBD-peptider testades och uppvisade en högre aktivitet mot Gram-negativa än mot Gram- positiva bakterier. Andra delen undersöker genuttryck av två immunförsvarsgener vid fågelinfluensainfektion. Vid genuttrycksstudier är resultatet till viss del beroende av stabiliteten hos de referensgener (RG) som används för normalisering av data. Därför behöver dessa validerades innan användning vid genuttrycksstudier. Elva potentiella RG testades och uppvisade varierande uttryck i olika vävnader hos gräsand, vilket visar vikten av att testa stabiliteten för den specifika experimentuppställningen. Baserat på dessa resultat användes referensgenerna i ett experiment där genuttrycket av retinoic acid inducible gene 1 (RIG-I) och myxovirus resistance gene (Mx) undersöktes i gräsänder infekterade med fågelinfluensavirus. Båda generna uppvisade en snabb och övergående uppreglering, där genuttrycket återgick till bakgrundsnivåer två dagar efter infektionsstart i nästan alla analyserade vävnader. Denna avhandling ger nya insikter om genetisk diversitet och evolution hos AvBD-gener i gräsand. Den tredimensionella strukturen av AvBD3b bidrar till ökad kunskap om AvBD-strukturer då endast några få defensinstrukturer från fåglar tidigare bestämts. Avhandlingen visar även på vikten av att undersöka stabiliteten hos potentiella referensgener för att få pålitliga resultat vid expressionsstudier samt att generna RIG-I och Mx är involverade under den tidiga immunresponsen vid fågelinfluensavirusinfektion i gräsänder. Nyckelord: Avian -defensins (AvBD), Genuttryck, Gräsand (Anas platyrhynchos), Immunförsvar, Immungener, Myxovirus resistant gene (Mx), Patogen, Retinoic acid inducible gene 1 (RIG-I) “Be like a duck. Remain calm on the surface and paddle like hell underneath.” - Michael Caine Table of contents List of papers ..................................................................................................... 3 My contribution to the individual papers ...................................................... 4 Abbreviations ................................................................................................ 5 Introduction ....................................................................................................... 7 Immune system ............................................................................................. 8 Physical defenses .......................................................................................... 8 Innate immune system ................................................................................... 9 Pattern recognition receptors ................................................................... 10 Retinoic acid inducible gene 1 ................................................................ 10 Signaling ................................................................................................. 11 Effector mechanisms ............................................................................... 11 Antimicrobial peptides ............................................................................ 12 Myxovirus resistant gene ......................................................................... 14 Adaptive immune system ...........................................................................
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